1. Field of the Invention
The present invention relates to a joint for connecting coaxial pipes together and, more particularly, it relates to a joint for connecting coaxial pipes which if so arranged that a plurality of pipes of one of the coaxial pipes can be simultaneously connected with corresponding pipes of the other of the coaxial pipes, respectively, and the respective ones of the connected portions can be sealed by a single packing.
2. Description of the Prior Art
Heretofore, a construction for connecting one pipe to another pipe has been widely used and various joints for connecting the pipes have been developed and carried into practical use. Furthermore, some constructions have been practically used to connect coaxial pipes together. The coaxial pipe has been employed with various purposes. With reference to a double pipe including an inner pipe and an outer pipe, for example, it is utilized in the following manners.
(1) It is used to carry a combustible gas, a poisonous gas or other dangerous fluids. In this case, the inner pipe is used to carry the dangerous fluid, while the outer pipe is used as emergency means or leakage prevanting means for preventing the fluid from leaking outside when a leakage of the fluid may occure from the inner pipe owing to a damage thereof or the like.
(2) It is used as a heat exchanger. In this case, fluids at different temperatures are passed through the inner pipe and the outer pipe, so that a heat exchange is effected between these fluids.
(3) It is used to feed a high-temperature fluid. If a piping system in which the double pipe is used requires the provision of a heat insulation, the inner pipe is used to feed the high-temperature fluid, while the outer pipe is evacuated, thereby forming the heat insulation aroud the inner pipe.
In order to form the piping system, a connection has been heretofore employed to connect one double pipe with another double pipe. However there is no satisfactory joint for connecting the double pipes together and, in fact, it has been a usual practice to form the connection by firstly connecting the inner pipes of the one and the other double pipes by means of a single joint, fitting the outer pipes onto these inner pipes at a construction field and then connecting these outer pipes by welding or binding together.
O-rings are arranged at the connected portions of the inner and outer pipes of these double pipes to form seals between the respective double pipes and between the outer pipes and atmosphere.
We made investigation into the joints for the double pipes and found that the conventional joints have many problems to be solved.
It is firstly noted that in case where lengths of the pipes as prepared are not fit to a piping system to be constructed or in case where a welding of the pipes is not allowed owing to danger of fire, it is impossible to construct the piping system.
Secondly, the conventional construction requires the steps of connecting the inner pipes and the outer pipes, separately, and arranging the packings at the connected portions of the inner and outer pipes, respectively. Accordingly, even if the piping system was arranged as required, the attaching and detaching of the pipes involve many troubles.
Furthermore, the sealing is made by arranging the separate packings at the connected portions of the inner and outer pipes, respectively, and the respective packings are subjected to deterioration at different rates from each other, owing to difference in durability of the respective packings, quality of the fluid and the other conditions. Accordingly, it is required to separately manage the sealed states of the respective connected portions of the inner and outer pipes, that is a troublesome job in actual the actual operation.